This invention relates generally to a path length control apparatus (PLC) for optical devices, and more specifically, to a PLC apparatus that includes an improved surface for reflecting laser beams within a ring laser gyroscope (RLG).
A ring laser gyroscope (RLG) is commonly used to measure the angular rotation of an object, such as an aircraft. Such a gyroscope has two counter-rotating laser light beams that propagate within a closed loop optical path or “ring” with the aid of successive reflections from multiple mirrors. The closed path is defined by an optical cavity that is interior to a gyroscope frame or “block.” In one type of RLG, the block includes planar top and bottom surfaces that are bordered by six planar sides that form a hexagon-shaped perimeter. The block is sometimes referred to as a laser block assembly. Three planar non-adjacent sides of the block form the mirror mounting surfaces for three mirrors at the corners of the optical path, which is triangular in shape.
Operationally, upon rotation of the RLG about its input axis (which is perpendicular to and at the center of the planar top and bottom surfaces of the block), the effective path length of each counter-rotating laser light beam changes. A frequency differential is produced between the beams that is nominally proportional to angular rotation. This differential is then optically detected and measured by signal processing electronics to determine the angular rotation of the vehicle. To maximize the signal out of the RLG, the path length of the counter-rotating laser light beams within the cavity must be adjusted. Thus, RLGs typically include a path length control apparatus (PLC), the purpose of which is to control the path length for the counter-rotating laser light beams to maximize the output signal.
Such PLCs typically include a piezoelectric transducer (PZT) secured to a mirror that is in turn secured to a mirror mounting surface of the laser block assembly (LBA). The mirror is in communication with bores in an optical cavity of the LBA. The bores form a portion of the closed loop optical path or ring defined by the optical cavity. The mirror reflects the counter-rotating laser light beams at its respective corner of the closed loop optical path. As such, a flatness of the mirror can affect the reflection of the counter-rotating laser light beams and thus operation of the RLG.